Friday, October 05, 2007

The Younger Dryas, Celestial Impacts, and Scarborough Bluffs

When scientists, even pretend ones like Dennis Quaid in "The Day After Tomorrow", talk about Global Warming leading to a new Ice Age, they usually refer to the 1,500 year period between about 13,000 and 11,500 years ago, known as the Younger Dryas, as evidence. During this time the mean annual temperature, which had been gradually increasing for several thousand years, dropped suddenly to levels more typical of the Last Glacial Maximum (see graph above).

What caused the Younger Dryas? The conventional wisdom is that, as the planet gradually warmed and the glaciers retreated, proglacial lakes were formed by the water melting from them. The largest of these was Lake Agassiz, which is theorised to have been at the very center of the continent (around present day Lake Winnipeg). Another was Lake Algonquin, which comprised most of the current great lakes, Georgian Bay, and parts of Northern Michigan. And a third was Lake Iroquois, which was an enlarged version of Lake Ontario.

For most of its existence, drainage from Lake Agazziz was Southward into the proto-Mississippi. Lake Algonquin flowed South towards the Gulf of Mexico, and Lake Iroquois drained South into the Hudson River. However, as the glaciers retreated (so the story goes), the ice-dam which prevented water from these lakes from flowing Eastward collapsed abruptly. An immense pulse of cold, fresh water flowed down the St. Lawrence Valley and out into the Atlantic, where it caused a shut-down of the North Atlantic thermocline (sometimes called the great ocean conveyor) which carries warm water Northward via the Gulf Stream. This in turn caused Northern Hemisphere temperatures to plunge, glaciers to advance again, and so on and so forth.

If you live in the Greater Toronto Area you can actually find evidence of the aftermath of this ice dam collapse in the form of Scarborough Bluffs. These bluffs are made of packed clay soil and in fact constitute the shore-line of old Lake Iroquois; previous to the great Eastward outflow which drained all of these pro-glacial lakes, the waters stood about 100 feet higher than today.

However, a new theory has come onto the scene. A recent paper has suggested (backed by some pretty good evidence) that an "impact event" occurred somewhere near the Great Lakes at the beginning of the Younger Dryas:

So did the cooling associated with this impact trigger the Younger Dryas? Probably not on its own. Though enough soot from the fires, and dust from the impact, would have been thrown into the atmosphere to significantly cool the climate, these effects would only have lasted several years. It is more likely that the impact caused a "destabilization/melting" of North America's interior ice sheets--including the bust up of that ice dam--which triggered that massive Eastward outflow from our pro-glacial lakes, and so on and so forth.

Now, why did I just write all this? Well, if you encounter a skeptic who tells you that its all bullshit because how can warming produce colder temperatures? you can tell them about the Younger Dryas. Of course, when scientists talk about the possibility of a Gulf Stream shut-down caused by modern day warming, they are looking at an entirely different mechanism: cold fresh water melting from the Greenland Ice Sheet, for the most part, bringing about the same effect.

MOSCOW, October 1 (RIA Novosti) - An asteroid, discovered in 2004, could pose a threat to Earth in 2029, the director of the Institute of Astronomy said Monday.

Boris Shustov said at an international space forum in Moscow that the Apophis asteroid, which is due to cross earth's orbit in 2029 at a height of 27,000 km (17,000 miles), could under certain conditions hit Earth in 2029.

The explosion could surpass the famous Tunguska explosion of June 30, 1908, which affected a 2,150 square kilometer (830 sq miles) area of Russia felling over 80 million trees in the Krasnoyarsk Territory in Siberia.

Or http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2007/10/04/sciaster104.xml

Oh the amplitude of uncertainty of thehe intersection is around 55000 km due to the n/body problem

no one is disputing that climate has always changed and always will. Hide your denier heads behind the obvious, as though you are making a point, but we are accelerating that change and the longer that is denied, the more we accelerate the changes. The faster climate changes, the harder it is to prepare for the changes.(how, how, how many times do we have to repeat this simple concept that grade school students understand?)